A communication device such as an RF receiver includes a signal amplifier circuit for amplifying received signals. In such a communication device, it is critical to increase the S/N ratio by reducing noise. However, the signal amplifier circuit is a noise source, and therefore, the noise generated from the signal amplifier when a received signal is amplified is superimposed on the signal. Patent Document 1 discloses a technology for reducing noise generated from the signal amplifier in such a communication device.
FIG. 6 is a diagram for explaining a conventional noise reduction technology according to Patent Document 1.
The circuit shown in the drawing includes: a first amplifier Ap1 that is connected to an input node and generates a first intermediate signal; a feedback resistor Rf that enables feedback of the first intermediate signal to the input node; a first attenuator At1 that receives the first intermediate signal and generates a second intermediate signal; a second attenuator At2 that is connected to the input node and generates a third intermediate signal; a second amplifier Ap2 that receives the third intermediate signal and generates a fourth intermediate signal; and an adder Σ that generates an output signal, using the second intermediate signal and the fourth intermediate signal. The output signal is substantially free of any noise component from the first amplifier Ap1.